1. Field of the Invention
The present invention relates to a fuel injector for an internal combustion engine and to a method for manufacturing such injector.
2. Disclosure Information
The manufacturing of fuel injection nozzles for internal combustion engines has historically been marked by the use of time consuming and laborious grinding, fitting and lapping operations. For example, the needles of fuel injectors are typically ground and lapped to fit into the valve bodies of the injectors. In some cases, the parts are ground separately and then fitted according to their finished sizes. In either event, it is necessary that the mated valve body and injector needle be handled as a unit due to the lack of interchangeability of parts.
U.S. Pat. No. 3,468,008 to Barber and U.S. Pat. No. 3,791,591 to Hedges disclose fuel injectors having traditional designs in which the needle is separable from the valve body. Because both components must be handled as a unit, special processing procedures which add to the cost of manufacturing must be used. According to the present invention, a fuel injector valve unit is assembled by permanently mating a valve needle to a valve body by caging the needle to the body in the manner shown herein. Because the needle, once caged to the valve body, is permanently attached thereto, no special handling is required to assure that the parts do not become mismatched after the needle and valve body have been mated.
A method according to another aspect of the present invention is intended to further reduce the cost of producing fuel injectors by eliminating the need for lift grinding during the manufacturing of such injectors. Lift grinding is a process by which the stroke of the injector is set. Lift grinding involves the use of relatively large grinding machines and delicate measuring equipment to measure, grind and establish a desired distance between a control surface on the valve body and a control surface on the valve's needle. Unfortunately, problems abound with this method of manufacturing. For example, the large size of the grinding machines renders fine tolerances difficult to achieve. This in turn causes uncertainties and variabilities in the stroke of the injectors.
According to conventional techniques, the desired air gap setting between the injector's armature and corresponding magnetic pole piece is established by measuring the dimensions of actual injector subassemblies and by performing calculations using the measured values to determine the thickness of a stop plate which functions as a shim to space the valve group from either the injector's inlet tube or some other internal abutment structure. This stop plate is selected from a group comprising as many as five dozen or more different thicknesses. Unfortunately, the multiplication of measurement errors plus finite differences in actual and nominal stop plate thicknesses results in large air gap variations. Also, stop plates in conventional injectors may become cocked or tilted such that the surface of the stop plate which contacts the injector needle in its fully opened position is not normal to the central axis of the injector needle. This condition may lead to wear and inaccurate stroke setting of the injector because the stroke can change as the needle wears into the stop plate. This is caused by high unit loading of the needle into the cocked stop plate.
The method and structure of the present invention solves all of the previously described problems with injector manufacturing. Because lift grinding is eliminated, the inaccuracies in stroke setting associated therewith are obviated. Because shims of varying thicknesses are not necessary with the present injector, the injector air gap may be set to the desired value precisely without the associated cumbersome and potentially inaccurate procedures associated with the selection of shims or spacers of different thickness. Accordingly, it is an object of the present invention to provide a method for manufacturing an injector which produces superior results in terms of reducing injector stroke and air gap variability, ease of manufacturing, and cost of the end item.
Other objects, features and advantages of the present invention will become apparent to those reading this specification.